DOCSLIB.ORG

Every Separable Complex Fréchet Space with a Continuous Norm Is Isomorphic to a Space of Holomorphic Functions

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Every Separable Complex Fréchet Space with a Continuous Norm Is Isomorphic to a Space of Holomorphic Functions Every separable complex Fr´echet space with a continuous norm is isomorphic to a space of holomorphic functions Jos´eBonet Abstract Extending a result of Mashreghi and Ransford, we prove that every complex sep- arable infinite dimensional Fr´echet space with a continuous norm is isomorphic to a space continuously included in a space of holomorphic functions on the unit disc or the complex plane, which contains the polynomials as a dense subspace. As a con- sequence examples of nuclear Fr´echet spaces of holomorphic functions without the bounded approximation exist. 1 Introduction. Let G be an open connected domain in the complex plane C. We denote by H(G) the Fr´echet space of holomorphic functions on G, endowed with the topology of uniform conver- gence on compact subsets of G. A Fr´echet space E of holomorphic functions on the domain G is a Fr´echet space that is a subset of H(G), such that the inclusion map E ⊂ H(G) is continuous and E contains the polynomials. By the closed graph theorem, the inclusion map E ⊂ H(G) is continuous if and only if the point evaluations at the points of G are continuous on E. If the polynomials are dense in E, then E is separable. The set P of polynomials is dense in H(G) if and only if G is the whole complex plane or a simply connected domain; see [15, Theorem 13.11]. However, this assumption is not needed in our results below. Banach spaces of holomorphic functions on the unit disc D and on the complex plane C have been thoroughly investigated. We refer the reader for example to the books [8], [19] and [20]. H¨ormander Fr´echet algebras of entire functions [2], [3], [12], the Fourier-Laplace transform of spaces of (ultra)-distributions [7] and intersections of growth Banach spaces [5], [8] are natural examples of Fr´echet spaces of holomorphic func- arXiv:2002.12677v1 [math.FA] 28 Feb 2020 tions. Vogt [18] proved that there are Fr´echet spaces E which are contained in H(G) such that the inclusion E ⊂ H(G) is not continuous. These examples are not Fr´echet spaces of holomorphic functions on G in our sense. Very recently, Mashreghi and Ransford [11, The- orem 1.3] have shown that every separable, infinite-dimensional, complex Banach space Y is isometrically isomorphic to a Banach space of holomorphic functions X ⊂ H(D) such that the polynomials are dense in X. The purpose of this note is to extend this result to the setting of Fr´echet spaces and to derive a few consequences. Our notation for functional analysis, in particular for Fr´echet spaces and their duals, is standard. We refer the reader to [9], [10], [13] and [14]. If E is a Fr´echet space, its topological dual is denoted by E′. The weak topology on E is denoted by σ(E, E′) and the weak* topology on E′ by σ(E′, E). The linear span of a subset A of E is denoted by span(A). In what follows, we set N0 := N ∪ {0}. 2020 Mathematics Subject Classification. Primary: 46A04, secondary: 46A11, 46A32. Key words and phrases. Spaces of holomorphic functions, Fr´echet spaces, continuous norm, bounded approximation property 1 2 Results. We start with the following observation. If a Fr´echet space F is isomorphic to a Fr´echet space E ⊂ H(G) of holomorphic functions on an open connected domain G ⊂ C, then F has a continuous norm. Indeed, let T : F → E be a topological isomorphism and let K ⊂ G be an infinite compact set. Since both T and the inclusion E ⊂ H(G) are continuous by assumption, there is a seminorm p on F such that supz∈K |T (x)(z)|≤ p(x) for each x ∈ F . If p(x) = 0 for some x ∈ F , then T (x)(z) = 0 for each z ∈ K. Therefore, the holomorphic function T (x) vanishes on G. Since T is injective, x = 0. We need the following Lemma to prove our main result. Lemma 2.1 Let F be a separable, infinite dimensional Fr´echet space with a continuous ′ ′ norm. Then one can find two sequences (en)n∈N0 ⊂ F and (en)n∈N0 ⊂ F such that (i) span{en | n ∈ N0} is dense in F . ′ ′ (ii) (en)n∈N0 is equicontinuous in F . ′ ′ ′ (iii) span{en | n ∈ N0} is dense in (F ,σ(F F )). ′ ′ N ′ (iv) hen, emi = 0 if n 6= m and hen, eni = 1 for each n ∈ 0. That is, (en, en)n∈N0 is a biorthogonal system. Proof. We denote by τ the metrizable topology of the Fr´echet space F and by p the continuous norm on F . Let U := {x ∈ F | p(x) ≤ 1} be the unit ball of the norm p. The polar set U ◦ of U in F ′ coincides with {u ∈ F ′ | |u(x)| ≤ p(x) for all x ∈ F } and, by ◦ ◦ ′ ′ Hahn-Banach theorem, its linear span H := span(U )= ∪s∈NsU is σ(F , F )-dense in F . Since (F,τ) is separable, there is a countable, infinite subset A = (yn)n∈N0 of F which is τ dense in F . Hence, A is also dense in the normed space (F,p), and this normed space is separable, too. The topological dual of (F,p) coincides with H = span(U ◦) ⊂ F ′. Since (F,p) is metrizable and separable, it follows from [14, Corollary 2.5.13] that H is σ(H, F )- ′ separable. We select a countable, infinite subset A = (vn)n∈N0 of H which is dense in (H,σ(H, F )). We now apply [14, Proposition 2.3.2] to find sequences (xn)n∈N0 ⊂ span(A) ′ ′ ′ ′ and (xn)n∈N0 ⊂ span(A ) such that hxn,xmi = 0 if n 6= m and hxn,xni = 1 for each N N ′ N ′ n ∈ 0, and span({xn,n ∈ 0}) = span(A) and span({xn,n ∈ 0}) = span(A ). N ′ ′ ◦ N Since for each n ∈ 0 we have xn ∈ span(A ) ⊂ H = ∪s∈NsU , then for each n ∈ 0 we ′ ′ −1 ′ can select m(n) > 0 such that |xn(x)|≤ m(n)p(x) for each x ∈ F . We set en := m(n) xn and en := m(n)xn for each n ∈ N0 and we check that these sequences satisfy properties (i) − (iv). (i) span({en,n ∈ N0}) = span({xn,n ∈ N0}) = span(A) is dense in (F,τ). ′ N ′ (ii) |en(x)|≤ p(x) for each x ∈ F and each n ∈ 0. Therefore, (en)n∈N0 is equicontin- uous in F ′. ′ N ′ N ′ (iii) span({en,n ∈ 0}) = span({xn,n ∈ 0}) = span(A ) is σ(H, F )-dense in H. Since ′ ′ N ′ ′ H is σ(F , F )-dense in F , we conclude that span{en,n ∈ 0} is σ(F , F )-dense in F . ′ (iv) This follows easily from the definitions, since (xn,xn)n∈N0 is a biorthogonal system. ✷ Lemma 2.1 is a version for separable Fr´echet spaces with a continuous norm of [6, Lemma 2], which was relevant in linear dynamics. See also [1, Lemma 2.11]. Observe that ′ ′ the existence of a sequence (en)n∈N0 ⊂ F satisfying (ii) and (iii) in Lemma 2.1 implies that the space F has a continuous norm. In fact, by (ii) there is a seminorm p on F such 2 ′ that supn∈N0 |en(x)| ≤ p(x) for all x ∈ F . Suppose that p(y) = 0 for some y ∈ F . Then ′ N en(y) = 0 for each n ∈ 0. Condition (iii) implies that y = 0. The statement and proof of our next result are inspired by Mashreghi and Ransford [11, Theorem 1.3]. Theorem 2.2 Let F be a separable, infinite dimensional, complex Fr´echet space with a continuous norm. Let G be an open connected domain in C. Then there exists a Fr´echet space E ⊂ H(G) of holomorphic functions on G such that F is isomorphic to E and the polynomials are dense in E. Proof. We apply Lemma 2.1 to the space F to select the sequences (en)n∈N0 ⊂ F and ′ ′ (en)n∈N0 ⊂ F satisfying conditions (i)−(iv). In particular, we find a continuous norm p on ′ N F such that |en(x)|≤ p(x) for each x ∈ F and each n ∈ 0. Now take a sequence (αn)n∈N0 ∞ n of positive numbers such that Pn=0 αnk < ∞ for each k ≥ 1. Define T : F → H(G) ∞ ′ n by T (x)(z) := Pn=0 αnen(x)z for each x ∈ F and each z ∈ G. The operator T is well- defined, linear and continuous. First of all, the series defining T (x) converges and defines an entire function for each x ∈ F , since ∞ ∞ ′ n n X αn|en(x)||z| ≤ p(x) X αnk < ∞ n=0 n=0 for each |z| ≤ k and each k ≥ 1. The continuity of T can be seen as follows: given an arbitrary compact subset L of G, there is k ≥ 1 such that |z| ≤ k for each z ∈ L. Then, for each x ∈ F we get ∞ ∞ ′ n n sup |T (x)(z)| = sup X αnen(x)z ≤ X αnk p(x). ∈ ∈ z L z L n=0 n=0 ′ Moreover, the map T is injective. Indeed, if T (x)=0in H(G), then en(x) = 0 for each ′ ′ ′ n ∈ N0. Since span({en | n ∈ N0}) is dense in (F ,σ(F , F )), this implies that x = 0. −1 n The monomials are clearly contained in T (F ), because T ((αn) en) = z for each N s n s −1 n ∈ 0.
Load more

Recommended publications
  • Intrinsic Volumes and Polar Sets in Spherical Space
    1 INTRINSIC VOLUMES AND POLAR SETS IN SPHERICAL SPACE FUCHANG GAO, DANIEL HUG, ROLF SCHNEIDER Abstract. For a convex body of given volume in spherical space, the total invariant measure of hitting great subspheres becomes minimal, equivalently the volume of the polar body becomes maximal, if and only if the body is a spherical cap. This result can be considered as a spherical counterpart of two Euclidean inequalities, the Urysohn inequality connecting mean width and volume, and the Blaschke-Santal´oinequality for the volumes of polar convex bodies. Two proofs are given; the first one can be adapted to hyperbolic space. MSC 2000: 52A40 (primary); 52A55, 52A22 (secondary) Keywords: spherical convexity, Urysohn inequality, Blaschke- Santal´oinequality, intrinsic volume, quermassintegral, polar convex bodies, two-point symmetrization In the classical geometry of convex bodies in Euclidean space, the intrinsic volumes (or quermassintegrals) play a central role. These functionals have counterparts in spherical and hyperbolic geometry, and it is a challenge for a geometer to find analogues in these spaces for the known results about Euclidean intrinsic volumes. In the present paper, we prove one such result, an inequality of isoperimetric type in spherical (or hyperbolic) space, which can be considered as a counterpart to the Urysohn inequality and is, in the spherical case, also related to the Blaschke-Santal´oinequality. Before stating the result (at the beginning of Section 2), we want to recall and collect the basic facts about intrinsic volumes in Euclidean space, describe their noneuclidean counterparts, and state those open problems about the latter which we consider to be of particular interest.
    [Show full text]
  • On Modified L 1-Minimization Problems in Compressed Sensing Man Bahadur Basnet Iowa State University
    Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2013 On Modified l_1-Minimization Problems in Compressed Sensing Man Bahadur Basnet Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Applied Mathematics Commons, and the Mathematics Commons Recommended Citation Basnet, Man Bahadur, "On Modified l_1-Minimization Problems in Compressed Sensing" (2013). Graduate Theses and Dissertations. 13473. https://lib.dr.iastate.edu/etd/13473 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. On modified `-one minimization problems in compressed sensing by Man Bahadur Basnet A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Major: Mathematics (Applied Mathematics) Program of Study Committee: Fritz Keinert, Co-major Professor Namrata Vaswani, Co-major Professor Eric Weber Jennifer Davidson Alexander Roitershtein Iowa State University Ames, Iowa 2013 Copyright © Man Bahadur Basnet, 2013. All rights reserved. ii DEDICATION I would like to dedicate this thesis to my parents Jaya and Chandra and to my family (wife Sita, son Manas and daughter Manasi) without whose support, encouragement and love, I would not have been able to complete this work. iii TABLE OF CONTENTS LIST OF TABLES . vi LIST OF FIGURES . vii ACKNOWLEDGEMENTS . viii ABSTRACT . x CHAPTER 1. INTRODUCTION .
    [Show full text]
  • Extension of Compact Operators from DF-Spaces to C(K) Spaces
    Applied General Topology c Universidad Polit´ecnica de Valencia @ Volume 7, No. 2, 2006 pp. 165-170 Extension of Compact Operators from DF-spaces to C(K) spaces Fernando Garibay Bonales and Rigoberto Vera Mendoza Abstract. It is proved that every compact operator from a DF- space, closed subspace of another DF-space, into the space C(K) of continuous functions on a compact Hausdorff space K can be extended to a compact operator of the total DF-space. 2000 AMS Classification: Primary 46A04, 46A20; Secondary 46B25. Keywords: Topological vector spaces, DF-spaces and C(K) the spaces. 1. Introduction Let E and X be topological vector spaces with E a closed subspace of X. We are interested in finding out when a continuous operator T : E → C(K) has an extension T˜ : X → C(K), where C(K) is the space of continuous real functions on a compact Hausdorff space K and C(K) has the norm of the supremum. When this is the case we will say that (E,X) has the extension property. Several advances have been made in this direction, a basic resume and bibliography for this problem can be found in [5]. In this work we will focus in the case when the operator T is a compact operator. In [4], p.23 , it is proved that (E,X) has the extension property when E and X are Banach spaces and T : E → C(K) is a compact operator. In this paper we extend this result to the case when E and X are DF-spaces (to be defined below), for this, we use basic tools from topological vector spaces.
    [Show full text]
  • Appropriate Locally Convex Domains for Differential
    PROCEEDINGS OF THE AMERICAN MATHEMATICAL SOCIETY Volume 86, Number 2, October 1982 APPROPRIATE LOCALLYCONVEX DOMAINS FOR DIFFERENTIALCALCULUS RICHARD A. GRAFF AND WOLFGANG M. RUESS Abstract. We make use of Grothendieck's notion of quasinormability to produce a comprehensive class of locally convex spaces within which differential calculus may be developed along the same lines as those employed within the class of Banach spaces and which include the previously known examples of such classes. In addition, we show that there exist Fréchet spaces which do not belong to any possible such class. 0. Introduction. In [2], the first named author introduced a theory of differential calculus in locally convex spaces. This theory differs from previous approaches to the subject in that the theory was an attempt to isolate a class of locally convex spaces to which the usual techniques of Banach space differential calculus could be extended, rather than an attempt to develop a theory of differential calculus for all locally convex spaces. Indeed, the original purpose of the theory was to study the maps which smooth nonlinear partial differential operators induce between Sobolev spaces by investigating the differentiability of these mappings with respect to a weaker (nonnormable) topology on the Sobolev spaces. The class of locally convex spaces thus isolated (the class of Z)-spaces, see Definition 1 below) was shown to include Banach spaces and several types of Schwartz spaces. A natural question to ask is whether there exists an easily-char- acterized class of D-spaces to which both of these classes belong. We answer this question in the affirmative in Theorem 1 below, the proof of which presents a much clearer picture of the nature of the key property of Z)-spaces than the corresponding result [2, Theorem 3.46].
    [Show full text]
  • Barrelled Locally Convex Spaces, North-Holland, Amsterdam, 1987
    PDF hosted at the Radboud Repository of the Radboud University Nijmegen The following full text is a publisher's version. For additional information about this publication click this link. http://hdl.handle.net/2066/60086 Please be advised that this information was generated on 2021-10-02 and may be subject to change. DEPARTMENT OF MATHEMATICS UNIVERSITY OF NIJMEGEN The Netherlands BARRELLED-LIKE SPACES IN p-ADIC ANALYSIS C. Perez-Garcia and W.H. Schikhof Report No. 9702 (January 1997) DEPARTMENT OF MATHEMATICS UNIVERSITY OF NIJMEGEN Toernooiveld 6525 ED Nijmegen The Netherlands BARRELLED-LIKE SPACES IN p-ADIC ANALYISIS C. Perez-Garcia*and W.H. Schikhof Abstract Several notions of barrelledness for locally convex spaces over non-archimedean valued fields are discussed in this paper and the relation between them is stud­ ied, We give examples showing that they are different notions in general. In particular, we solve (Theorem 2.6) the question raised by the second author in [13]: Do there exist polar spaces that are polarly barrelled but not barrelled?. On the other hand, the concepts of orthogonality as well as elementary and edged set are used to prove that for a wide class of spaces of countable type the different versions of barrelled spaces considered in the paper coincide. We obtain in this way (and with different proofs) the non-archimedean counterparts of well-known results in the theory of barrelled spaces over the real or complex field. 1991 Mathematics Subject:46SlO. INTRODUCTION Like in the classical case (i.e., locally convex spaces over the real or complex field see e.g.
    [Show full text]
  • Completeness and the Open Mapping Theorem Bulletin De La S
    BULLETIN DE LA S. M. F. VLASTIMIL PTÁK Completeness and the open mapping theorem Bulletin de la S. M. F., tome 86 (1958), p. 41-74 <http://www.numdam.org/item?id=BSMF_1958__86__41_0> © Bulletin de la S. M. F., 1958, tous droits réservés. L’accès aux archives de la revue « Bulletin de la S. M. F. » (http: //smf.emath.fr/Publications/Bulletin/Presentation.html) implique l’accord avec les conditions générales d’utilisation (http://www.numdam.org/ conditions). Toute utilisation commerciale ou impression systématique est constitutive d’une infraction pénale. Toute copie ou impression de ce fichier doit contenir la présente mention de copyright. Article numérisé dans le cadre du programme Numérisation de documents anciens mathématiques http://www.numdam.org/ Bull. Soc. math. France^ 86, IQ58, p. 4i a 74. COMPLETENESS AND THE OPEN MAPPING THEOREM; BY VLASTIMIL PTAR, (Praha). 1. Introduction. — In the present paper we intend to give an account of some investigations concerned with the open mapping theorem. The starting point of these investigations was the natural desire to understand what is at the back of this theorem which, undoubtedly, is one of the deepest in functional analysis. Their final aim is to clear this result of unnecessary assumptions — especially that of the metrizability of the spaces in question — and to extend it to as wide a class of topological linear spaces as possible. These investigations have led quite naturally to the introduction of what we believe to be an interesting notion — namely the notion of ^-complete- ness, which coincides with ordinary completeness in metrizable spaces and which is strong enough to ensure the validity of the open mapping theorem in the general case.
    [Show full text]
  • Arxiv:2107.04662V1 [Math.GN]
    ON LINEAR CONTINUOUS OPERATORS BETWEEN DISTINGUISHED SPACES Cp(X) JERZY KA¸KOL AND ARKADY LEIDERMAN Abstract. As proved in [16], for a Tychonoff space X, a locally convex space Cp(X) is distinguished if and only if X is a ∆-space. If there exists a linear con- tinuous surjective mapping T : Cp(X) → Cp(Y ) and Cp(X) is distinguished, then Cp(Y ) also is distinguished [17]. Firstly, in this paper we explore the following question: Under which con- ditions the operator T : Cp(X) → Cp(Y ) above is open? Secondly, we devote a special attention to concrete distinguished spaces Cp([1, α]), where α is a countable ordinal number. A complete characterization of all Y which admit a linear continuous surjective mapping T : Cp([1, α]) → Cp(Y ) is given. We also observe that for every countable ordinal α all closed linear subspaces of Cp([1, α]) are distinguished, thereby answering an open question posed in [17]. Using some properties of ∆-spaces we prove that a linear continuous sur- jection T : Cp(X) → Ck(X)w, where Ck(X)w denotes the Banach space C(X) endowed with its weak topology, does not exist for every infinite metrizable compact C-space X (in particular, for every infinite compact X ⊂ Rn). 1. Introduction ′ A locally convex space (lcs) E is called distinguished if its strong dual Eβ = (E′, β(E′, E)) is a barrelled space. A. Grothendieck [11] proved that a metrizable ′ lcs is distinguished if and only if Eβ is bornological. Also, if all bounded subsets of ′ the strong dual Eβ of a metrizable lcs are metrizable, then E is distinguished [11].
    [Show full text]
  • Arxiv:Math/0501187V1
    ON KERNEL THEOREMS FOR FRECHET´ AND DF SPACES A. G. SMIRNOV AND M. A. SOLOVIEV Abstract. A convenient technique for calculating completed topological ten- sor products of functional Fr´echet or DF spaces is developed. The general construction is applied to proving kernel theorems for a wide class of spaces of smooth and entire analytic functions. Let X and Y be sets and F , G, and H be locally convex spaces consisting of func- tions defined on X, Y , and X × Y respectively. If the function (x, y) → f(x)g(y) belongs to H for any f ∈ F and g ∈ G, then F ⊗ G is identified with a lin- ear subspace of H. In applications, it is often important to find out whether H can be interpreted as the completion of F ⊗ G with respect to some natural ten- sor product topology. Results of this type (or, more often, their reformulations in terms of one or other representations for continuous bilinear forms defined on F × G) for concrete functional spaces are known as kernel theorems. For example, Schwartz’s kernel theorem for tempered distributions amounts to the statement that the space S(Rk1+k2 ) of rapidly decreasing smooth functions on Rk1+k2 is iden- k1 k2 k1 k2 tical to the completion S(R )⊗πS(R ) of S(R ) ⊗ S(R ) with respect to the projective1 topology. Very general conditions ensuring the algebraic coincidence of H with F ⊗πG can be derived fromb the description of completed tensor products of functional spaces given by Grothendieck ([3], Chapitre 2, Th´eor`eme 13).
    [Show full text]
  • Notes for Functional Analysis
    Notes for Functional Analysis Wang Zuoqin (typed by Xiyu Zhai) Nov 3, 2015 1 Lecture 15 1.1 The weak ∗-topology on X∗ Let X be a topological vector space. We want to topologize the dual space X∗ (in a natural way) to make it a (nice) topological vector space. We have seen that if X is a normed vector space, then there is a natural way to assign a topology on X∗ to make it not just a topological vector space, but in fact a Banach space. The norm we assigned to X∗ is the operator norm kLkX∗ = sup jLxj: kxk=1 But this method does not work for more general topological vector spaces. We will study the norm topology on X∗ in more detail later. Today we will use the method of weak topology to construct a topology on X∗. Let X be any topological vector space (where we don't require X∗ to separate points). Then each x 2 X induces a linear ∗ functional evx on X , ∗ evx : X ! F;L 7! Lx (1) The linearity of evx is obvious: evx(αL1 + βL2) = (αL1 + βL2)(x) = αL1(x) + βL2(x) = αevx(L1) + βevx(L2): Moreover, ∗ Lemma 1.1. The family X = fevx : x 2 Xg separates \points" in X . ∗ Proof. For any L1 6= L2 2 X , one can find x0 2 X such that L1x0 6= L2x0: It follows that evx0 (L1) 6= evx0 (L2). 1 Definition 1.2. The X -topology of X∗ is called the weak-∗ topology. Remarks 1.3. • For any topological vector space X, the weak-∗ topology on X∗ makes X∗ a locally convex topological vector space.
    [Show full text]
  • Basic (And Some More) Facts from Convexity
    1 Basic (and some more) facts from Convexity In this chapter we will briefly collect some basic results and concepts con- cerning convex bodies, which may be considered as the main ”continuous” component/ingredient of the Geometry of Numbers. For proofs of the results we will refer to the literature, mainly to the books [2, 5, 6, 7, 9, 11, 13, 14], which are also excellent sources for further information on the state of the art concerning convex bodies, polytopes and their applications. As usual we will start with setting up some basic notation; more specific ones will be introduced when needed. n Let R = x =(x1,...,xn)| : xi R be the n-dimensional Euclidean { 2 } space, equipped with the standard inner product x, y = n x y , x, y h i i=1 i i 2 Rn. P For a subset X Rn,letlinX and a↵ X be its linear and affine hull, ✓ respectively, i.e., with respect to inclusions, the smallest linear or affine subspace containing X.IfX = we set lin X = 0 , and a↵ X = .The ; { } ; dimension of a set X is the dimension of its affine hull and will be denoted by dim X.ByX +Y we mean the vectorwise addition of subsets X, Y Rn, ✓ i.e., X + Y = x + y : x X, y Y . { 2 2 } The multiplication λX of a set X Rn with λ R is also declared vec- ✓ 2 torwise, i.e., λX = λ x : x X .Wewrite X =( 1) X, X Y = { 2 } − − − X +( 1) Y and x + Y instead of x + Y .
    [Show full text]
  • PDF Hosted at the Radboud Repository of the Radboud University Nijmegen
    PDF hosted at the Radboud Repository of the Radboud University Nijmegen The following full text is a publisher's version. For additional information about this publication click this link. http://hdl.handle.net/2066/57040 Please be advised that this information was generated on 2021-09-30 and may be subject to change. Groupe d'étude d'Analyse nitrmétrique 24-01 (Y. AI'iICE, G. CHRISTOL, P. ROBBA)I 12e année, 1984/85, n° 24, 33 p. 3 ju in 1S85 COIIVEX by Win H. SCHIKHOF ( ') Abstract» — A structure theory (part I) and a duality theory (part I I ) for local convex spae'es over ultrametrie nonspherically complete valued fields is developed. As an application nuclearity, reflexivity and the Hahn-Banach property are obtaine for certain classes of spaces of C- and analytic functions and their duals. Introduction. follow ing E over a non-archiuedean, nontrivially valued complete field R . {Let D be a subspace of’ E , let p be a continuous 3eninoru on S h let f € D’ \with |f ^ p on D . Then f has an extension f e E* such that f ^ p on E. The non-archinedeon Hahn-Banach theorec. ([143, Th, 3*5) states that (*) holds i f K is spherically (= maximally) complete. Froiu [ll] p. 91 & 92 it is not hard to * derive the following 'converse1. PROPOSITION. - Let K be not spherically complete. If E is Hausdorff and (*) is true dim E ^ 1 . The purpose of this paper i3 to show that, for certain classes of spaces over # nonspherically complete base fields, a satisfactory duality theory exists.
    [Show full text]
  • Separability of the L1-Space of a Vector Measure
    SEPARABILITY OF THE L'-SPACE OF A VECTOR MEASURE by WERNER J. RICKER (Received 22 June, 1990) Let 2 be a a-algebra of subsets of some set Q and let n :2—»[0, °°] be a a-additive measure. If 2(j*) denotes the set of all elements of 2 with finite jU-measure (where sets equal [i-a.e. are identified in the usual way), then a metric d can be defined in 2(ji) by the formula d(E, F) = n{E AF) =\\XE- XF\ dp (£, F e 2); (1) here £ AF = (E\F) U (F\E) denotes the symmetric difference of E and F. The measure ^ is called separable whenever the metric space (2(^t), d) is separable. It is a classical result that ju is separable if and only if the Banach space L'(ju) is separable [8, p. 137]. To exhibit non-separable measures is not a problem; see [8, p. 70], for example. If 2 happens to be the a-algebra of /z-measurable sets constructed (via outer-measure fi*) by extending H, defined originally on merely a semi-ring of sets Fcl, then it is also classical that the countability of T guarantees the separability of fi and hence, also of Ll(p), [8, p. 69]. There arises the natural question of what form such classical results on separability of Ll-spaces should take for vector-valued measures. We aim to formulate such results in this note. So, suppose that A' is a locally convex space (briefly, lcs), always assumed to be Hausdorff and sequentially complete.
    [Show full text]